Afterburners for cupola furnaces

ABSTRACT

An in-bed burner system and arrangement for stack furnaces wherein a series of burners are mounted on the stack below the charge door opening to direct a jet of burning gases into the stack below the top surface of the charge bed. Supplementary air is supplied to the stack from a position adjacent the burners to support relatively complete combustion of the products of combustion rising in the stack. Oxygen can augment or replace the supplementary air. The in-bed burners and supplementary air effect burnout of carbon monoxide in the stack exhaust gases and maintain a relatively high temperature in the top portions of the charged bed to thermally crack and burn out organic materials present in the charge.

United States Patent F rundl et al.

[4 1 May 30,1972

[54] AF TERBURNERS FOR CUPOLA FURNACES [72] Inventors: Ronald J. Frundl, Livonia; Victor W. Hanson, Westland; Robert M. Jamison, Detroit; Orlan M. Arnold, Grosse Pointe Park, all of Mich.

[73] Assignee: Ajem Laboratories, Inc., Livonia, Mich.

[22] Filed: Sept. 11, 1970 [21] Appl. No.: 71,463

Related US. Application Data [63] Continuation-impart of Ser. No. 707,250, Feb. 21,

1968, Pat. No. 3,545,918.

52 u.s.c|. ..263/29 51 1m.c| ..F27b 1 00 [58] FieldofSearch ..263/29,30; 266/25 3,l59,209 12/1964 Dailey, Jr ..263/29X Primary Examiner.lohn J. Camby Attorney-Curtis, Morris & Safiord [57] ABSTRACT An in-bed burner system and arrangement for stack furnaces wherein a series of burners are mounted on the stack below the charge door opening to direct a jet of burning gases into the stack below the top surface of the charge bed. Supplementary air is supplied to the stack from a position adjacent the burners to support relatively complete combustion of the products of combustion rising in the stack. Oxygen can augment or replace the supplementary air. The in-bed burners and supplementary air efiect burnout of carbon monoxide in the stack exhaust gases and maintain a relatively high temperature in the top portions of the charged bed to thermally crack and burn out organic materials present in the charge.

16 Claims, 4 Drawing Figures SHEET 10F 2 INVEN'IORS RONALD J. FRUNDL VICTOR W. HANSON ROBERT M. JAMISON ORLAN M.ARN o 6.42;, m

ATTORNEYS AFTERBURNERS FOR CUPOLA FURNACES This application is a continuation-in-part of our copending US Pat. Application Ser. No. 707,250 filed on February 21, 1968 (now issued as Pat. No. 3,545,918), and the disclosure of that patent application is incorporated herein by reference.

This invention relates to in-bed burner systems and more particularly to in-bed burner methods and apparatus for use with cupola furnaces, and in its broad aspects, with incinerators and the like.

Until recently, effluents from furnace stacks were commonly allowed to discharge directly into the atmosphere, thereby depositing dust on nearby areas. Typically these effluents were characterized by objectionable odors and a heavy black, brown, or reddish color. The characteristic smoke and odor were the result of iron oxide particles plus partially burned hydrocarbons. With the recently increased concern with air pollution and environmental protection many devices have been tried in conjunction with furnace stacks in an attempt to eliminate air pollution hazards. Among some of these air pollution control devices are bag filters, electrostatic precipitators, cyclone dust collectors, to remove ash dust, and air washers to clean and scrub particulate matter from the stack exhaust. These devices have been helpful, however, the more stringent air pollution control codes are requiring even more efficient systems and apparatus to remove a greater proportion and range of contaminants from furnace exhausts.

Afterburners positioned high up in furnace stacks have also been tried in an attempt to decrease air pollution but these were far from satisfactory. The positioning of some of the early designed afterburners high up in the stack was believed necessary in order to sustain continuous combustion since the composition of the gaseous products of combustion vary greatly and cause blow-out of the early afterbumer flame at lower elevations. Further, it has since been found that afterburners positioned above the charging opening burn the stack gases mixed with the unmetered air drawn in through the charging opening and thus the afterburner combustion varied constantly, resulting in poor efficiency. Also, the air drawn in through the charging opening had a cooling effect on the stack gasses adding to the inefficiency and usually causing the afterbumer combustion temperatures to be lowered sufficiently to not permit complete combustion of the carbon monoxide and high molecular weight organic residues.

The most seriously objectionable constituents in furnace exhaust gases are carbon monoxide (resulting from incomplete oxidation within the furnace itself) and various high molecular weight organic residues. In cupola furnaces, for example, these organic residues often result from the use of scrap metal in the furnace along with materials such as coke, flux and iron. On a great deal of this scrap metal, oil, greases and other organic materials including paint and like surface coatings are present in appreciable quantities.

These grease and paint resin components have a high molecular weight and are difficult to burn completely. As differences in temperature occur in different regions of the furnace itself, there is competition among the various components of the charge for the available oxygen, and many of the organic residues are only partially thermally cracked, decomposed and semi-oxidized to form numerous organic derivatives. Since most cupola furnaces utilize a rapid combustion process the materials do not remain in the furnace for a long period and even if the temperature is high, the oils and greases are distilled and thermally cracked but do not burn to carbon dioxide and water vapor.

Thus, these incompletely burned organic residues result in the formation of sub-micron liquid aerosols which are difficult to remove in any dust collection of air washing system and pass through to contaminate the atmosphere.

One method of overcoming these problems was disclosed in our above mentioned copending application utilizing afterburners installed at elevations above the charge bed and no higher than the rear and side portions of a furnace stack adjacent the charging opening such that the afterburner flame jets penetrate the area below the charge opening. By thus positioning the afterburners substantially complete combustion of effluent carbon monoxide and organic residue is attained since the exhaust gases are burned at their highest temperatures in the stack prior to the dilution and cooling effects caused by unmetered air entering the charge door opening and is aided by the heat from the combustion of the carbon monoxide.

While the afterburners described in our above mentioned application have proven to be a truly significant advance, it has been found desirable to obtain further increases in the efficiency of removal of air pollution products from furnace stacks and in particular in the complete burnout of the higher molecular weight materials. Applicant, having recognized the source of the continuing problem of incomplete combustion of high molecular weight residues, reasoned that the earlier efficient burning could be initiated, the longer would be the reaction time available to complete combustion before the residues were cooled by the air flowing in at the charge door. However, cupola furnace experts resisted this proposed solution because of feared adverse effects on the metallurgical process. Preliminary findings by applicant indicate that while the charge recipe may in fact change, there is an overall improvement in reduced processing time and in some cases reduced requirements for carbon in the charge without undue control problems and with reduced air pollution.

It is therefore an object of the present invention to provide a system in furnace stacks to consume more effectively the carbon monoxide in the effluent gases.

It is another object of the present invention to utilize the heat value of carbon monoxide within the cupola furnace before its escape up the stack and thereby effectively combust the organic residues with increased efficiency and with enhancement to the metallurgical process.

It is a still further object of the present invention to eliminate polluting aerosols previously escaping through large scale prior art air pollution control systems.

In accordance with a preferred embodiment of the present invention, a plurality of self-sustaining in-bed burner jets are arranged around the periphery of a furnace stack in positions below the charge door opening to direct the burner flame into the stack below the top surface of the charge bed. Advantageously, supplementary air is also supplied into the stack from positions adjacent the burners and appropriate control means are provided to vary the direction and volume of air supplied in accordance with the character of combustion products present in various sectors of the furnace stack. The control means can be preset for expected conditions, manually adjusted, or preferably automatically responsive to sensors monitoring conditions within the stack. The supplementary air may be advantageously augmented or replaced by pure oxygen, with appropriate adjustment of the hydrocarbon gas and coke charge to give the desired carbon content to the molten metal.

Advantages of the present invention include higher temperatures throughout the charge bed up to the charge door with consequently more rapid and more complete burnout resulting in less pollution and higher production rates. The higher temperatures and greater availability of oxygen burns out the carbon monoxide more completely and at a point where the BTUs thus generated are used directly in the metallurgical process and lost up the stack.

In the specification and in the accompanying drawings there are described and shown illustrative embodiments of the invention and various modifications thereof are suggested, but it is to be understood that these are not intended to be exhaustive, but on the contrary are given for purposes of illustration in order that others skilled in the art may fully understand the invention so that they may modify and adapt it in various forms, each as may be best suited to the conditions of a particular use.

The various objects, aspects and advantages of the present invention will be more fully understood from a consideration of the following specification in conjunction with the accompanying drawings in which:

FIG. 1 is a diagrammatic elevational view showing a furnace stack, a charging opening, and the position of the in-bed burners and supplementary air supply ducts;

FIG. 2 is an enlarged detailed view, partly in section showing an in-bed burner of the present invention;

FIG. 3 is a plan view of the supplementary air supply ducts; and

FIG. 4 is a diagrammatic sectional view similar to FIG. 1 of another embodiment of the present invention illustrating a typical charge bed composition during furnace operation.

Referring now to FIG. 1, there is shown a stack furnace 10. A row of tuyeres l2 introduces oxygen (typically as a portion of air) which is required for the formation of a melting zone in the charge contained within the furnace stack. A charging opening 14 allows for the introduction of the charge into the furnace itself. The furnace as illustrated is intended to represent a cupola furnace for the production of iron and steel. Thus, the charge supplied will include coke, iron ore, iron scrap and flux. While the present description of the invention relates primarily to cupola furnaces, it is noted that the principles involved in the present invention also apply to other stack furnaces, such as for example, incinerators, which operate under similar conditions. Such furnaces will also include a charge door and a charge composed of a porous material from which it is desired to remove air pollutants during furnace operation.

BACKGROUND The charge for the cupola furnace 10 is admitted through charging opening 14 in any suitable manner, e.g. by a skip hoist mechanical charging bucket forming alternate levels and 22 of fuel and iron, respectively. These charges drop down into the stack to form the charge bed. The composition of the charge bed during normal furnace operations is illustrated in FIG. 4 and is seen typically to include four relatively well defined zones of charge composition which are maintained in order that rapid and economical melting and production of iron will result. These zones include a lower crucible zone, a combustion or tuyere zone, a melting zone and what is termed, in the art, as a stack zone.

The crucible zone extends from the bottom of the cupola to the level of tuyeres 12. In this zone the iron and slag produced in the furnace collect after they have been melted and reduced and are discharged from the furnace through tap holes 16 which are vertically spaced to separate these products accord ing to their relative specific gravities. The tuyere zone is the portion of the charge bed in which a blast of oxygen or more typically oxygen-containing air, comes in contact with and burns the fuel which generally is composed substantially of coke. This is a combustion zone wherein all of the heat for the melting operation is produced by the combustion of the coke in the charge with the oxygen supplied from the tuyeres. The melting zone is immediately above the tuyere zone and is the space in which the melting of iron and in the charge takes lace. p As seen in FIG. 4, a level of iron is supported on a column of coke in the combustion zone, this coke being the only solid material in the charge bed below the melting zone. As the iron melts it flows down through the column of coke in the tuyere zone to the crucible portion of the stack. During the period in which the iron in a given layer 22 is melting, the column of coke beneath the melting zone is continuously burning and sinking. Therefore, a level of additional fuel 20 is interposed between each layer of iron 22 to provide a continuous supply of coke to the combustion zone. The layers of iron and coke are proportioned preferably such that each charge of iron will enter the top of the melting zone just before the previous charge is completely melted at the bottom of the melting zone and thus a continuous stream or iron will collect in the crucible zone and run from the tap holes 16. Also the coke burned from the column in the combustion zone will be replenished each time by the layer 22 of new coke coming down from the stack zone and thus the position of the melting zone will be substantially maintained in the area shown within generally constant limits.

The stack zone extends above the melting zone to substantially the level of the base of the charge door opening. This zone contains new charge material which will absorb some heat from the products of combustion flowing upwardly in the stack, and in addition, the stack zone insulates the melting zone to a certain extent to keep heat in the lower portions of the stack for the required metallurgical processes.

During operation of the cupola furnace, gaseous products of combustion are formed in the tuyere zone and rise in stack 10 through the charge bed to the top of the stack, from which they escape through air washing and dust collection systems (not shown).

PREFERRED EMBODIMENT In order to maintain a relatively constant high temperature throughout the upper charge level to produce a more complete combustion of carbon monoxide and to substantially completely burn out the organic materials present in the charge, a plurality of in-bed burner elements 30 are provided on the stack 10 in an area 32 below the bottom 34 of the charge door 14 wherein they will be located below the top surface 36 of the charge bed during normal furnace operation. By thus positioning the burners 30, heat is supplied to the charge to assure optimum temperature conditions for burning the carbon monoxide and this heat is supplied directly to the metallurgical operation rather than being dissipated to the at mosphere or the air cleaning equipment (as is the case when afterburners are operative only above the charge bed level). The specific distance at which burners 30 are located below the charge door may be varied depending on the diameter of the furnace and other operating conditions that may effect the ambient elevation of the top of the charge bed.

The carbon monoxide in the burning effluent gases has a high heat potential and, when bumed, supplies additional heat for thermally cracking and burning the organic materials in the charge which come principally from oil, grease, paints and other organic deposits on scrap material used in the metallurgical process. The desirable reaction to produce this additional heat is ZCOi O 2C0 heat. The reaction eliminates the undesirable carbon monoxide and produces relatively harmless carbon dioxide plus the desirable heat. As mentioned above, in normal cupola furnace operation there is a wide deviation in temperatures of the gases rising in the stack and the in-bed burners serve to maintain the desirable temperature levels for this reaction to take place. However, to assure a complete burnout of the carbon monoxide it is desirable to supply additional oxygen to the process from outside the furnace since the oxygen composition of gases coming up through the furnace at this level varies greatly and is normally insufficient for complete combustion. Accordingly, supplemental air supply ducts 38 are provided adjacent each of the in-bed burners 30 to provide the necessary additional oxygen.

The burners and supplemental air supply ducts thus located in positions below the top level of the charge bed, in addition to advantageously providing for more complete combustion of the carbon monoxide, elevate the stack gas temperature, due to the heat from the burners and from the combustion of carbon monoxide, to achieve a more complete thermal cracking of high molecular weight organic residues. The organic residues are thereby burned out more completely and the production of organic aerosols which, as mentioned above, are not readily removed from the efiluent by air washing equipment, are substantially eliminated. Additionally, the higher temperatures produced in the charge bed in the stack zone preheats the charge as it descends into the melting zone of the furnace bed and thereby improves the efficiency of the metallurgical reactions within the furnace itself.

Referring now to FIG. 2, there is shown a detail of an in-bed burner assembly 30 and supplemental air supply duct 38, it being understood that the other in-bed burners and air supply ducts positioned about furnace are of similar construction. Burner 30 is housed in an outer rectangular or circular jacket 40 which extends into the wall 42 of the cupola stack, and through its refractory lining 44, as well as through the outer casing 46 which may be constructed of steel or brick in the conventional manner. Burner jacket 40 includes an end cover plate 48 with the burner 50 extending through cover plate 48 and directed into the interior of the cupola stack through an opening 52 in wall 42 of stack 10.

Burner 50 is of generally cylindrical construction and has an inner sleeve portion 54 of greater diameter than outer portion 56 and is mounted within jacket 40 by means of a flange plate 58, carrying the exposed end 60 of the burner, which is bolted at 62, to the end plate 48 of the jacket.

A gas fuel supply line 64 provides the fuel gas for burner 50. A controlled supply of air under pressure is provided, from a blower (not shown) and an air supply line 66 to the burner 50, to form a jet stream through the burner element to assist in drawing the burner fuel gases into the burner and also to supply the air needed for burner combustion and initial mixing of air and burner fuel gas. A pilot 68 including ignitors (not shown) may be provided to supply fuel to ignite the gases in the burner.

Insulating refractory material 55 is disposed around the small diameter portion of burner 56 and additional refractory material 57 is interposed between the sleeve walls 40 and the burner element 50 to preclude unwanted heat transfer from the exposed portions of the burner.

It is noted that while burners 30 have been shown positioned in a generally horizontal plane it is foreseen that they may be inclined with respect to the vertical axis in the same manner as the afterbumers disclosed in our above mentioned copending application.

Additional air to support the combustion of carbon monoxide is supplied through an auxiliary air supply line 70 which communicates with the above mentioned air duct 38 positioned below the burner 30. Air duct 38 is formed as a generally flared housing 72 containing a plurality of separation walls 73 which define exhaust chambers 75. The housing extends through outer casing 46 of refractory lining 44 in cupola stack 10 and communicates with the interior of the stack through an opening 80 in wall 42.

While the supplementary air supply duct 38 is illustrated as being in a generally horizontal position below burner 30, it is foreseen that this duct may be otherwise adjacently positioned, e.g. in an inclined configuration. The angle of inclination in such case is governed by the volume of air desired to be introduced, and the timing of the mixing of the gases such as carbon monoxide with the oxygen supply before ignition by burners 30.

As mentioned above, the compositions of the effluent gases rising in the stack vary greatly within the different quadrants of the furnace bed. That is, the carbon monoxide content and the oxygen content of the efiluents may be substantially different in a given sector of the charge bed cross-section within the stack zone adjacent the in-bed burners. In order to properly control the mixing of carbon monoxide and oxygen for accomplishing full burnout below the top of the charge bed level, the air supply through housing 72 and chambers 75 must be regulated to distribute the air as required to various portions of the stack to insure proper mixing of the oxygen and gas. This is accomplished by the use of the multiple banks of damper blades or deflectors 76, 78 as shown in FIG. 3. The double damper system thus provided permits deflection of air flow through the various sectors of the stack and in addition regulates the amount of air supplied. The position of each of the various dampers is regulated by a control mechanism which may be pneumatically, hydraulically, or electrically operated, and which is responsive to the carbon monoxide content within various sectors of the cupola furnace. Each pair of dampers in a chamber 75 is separately controlled in order to direct the necessary amount of air to a different sector of the stack to support complete combustion of effluent carbon monoxide The control mechanism for dampers 76 and 78 may also include safety devices responsive to various furnace conditions which will automatically shut off the supply of air through the duct and in addition shut off burner 30 in the event that there is a blow out in the cupola furnace or any other hazardous condition which would be aggravated if burners 30 were to continue in operation.

While the above description of the preferred embodiment has shown the in-bed burner and supplemental air supply means as being positioned in the stack zone of the charge bed wherein the incoming charge is sufficiently porous so that the flame and supplied oxygen can readily flow into the entire mass of the charge, it is foreseen that the burner and air supply means may be positioned at even lower locations in the stack. For example, the burner and air supply means may be positioned in the area of the charge bed melting zone, in which case the pressure of the air supply must be somewhat higher in order to penetrate the relatively non-porous mass of the melting iron therein. In this location the additional heat produced by the combustion of carbon monoxide and oxygen will be supplied directly to the iron to assist in the melting thereof, and also to heat the products of combustion to higher temperatures which in turn preheat the charge in the stack zone to higher temperatures as they flow upwardly through the furnace.

It is noted that the air supplied to furnace 10 through duct 38 may be either relatively cool ambient air or preheated air. In the latter case the warm products of combustion discharged from furnace 10 may be passed through a heat exchanger to warm the ambient air prior to its admission to supply line 70. Supplementary air which is preheated in this manner aids in maintaining the high temperatures required for complete combustion of the carbon monoxide and organic materials.

Referring again to FIG. 4, there is shown a diagrammatic cross-section of a cupola furnace containing a charge bed therein as it is composed during normal operations of the furnace. In addition there is illustrated an arrangement in which the in-bed burners of the present invention are used in conjunction with afterbumers similar to those described in out above-noted copending application. The afterbumers 90 are positioned in locations around stack 10 near the charging opening 14 and are angled downwardly to introduce a flame to penetrate levels of the stack below the opening but above the furnace bed. In this manner temperatures in the stack above the charge bed are closely controlled to assist in more complete combustion of the carbon monoxide in the effluent gases. Fuel gas and air are supplied to afterbumers 90 through conduits 92 and 94 respectively to produce the required jet of burning gases. As explained in the prior application auxiliary air is supplied to the afterbumer through an auxiliary air supply line which communicates with a portion of burner housing 90 to introduce air into the cupola stack below the afterbumer for supplying additional oxygen as required for the combustion of carbon monoxide in the effluent gases. The additional air for afterbumers 90 in the construction illustrated in FIG. 4 is supplied through a conduit 96 from a main air distribution header 98. Conduit 96 may be provided with a gravity type damper 100 which effectively prevents inadvertent admissions of combustible products into supply conduit 96 and the air distribution system in the event that no air is being furnished to the afterburner from header 98. In addition conduit 96 may be provided with a second damper 102 which is connected to control means (not shown) responsive to furnace conditions which will automatically shut off the supply of air to the burner in the event that the afterbumers fail or are shut off. Other control units may also be provided, as described in our above noted application, which will automatically shut off the afterburner in the event that there is a hazardous condition within the furnace which would be aggravated if the afterbumer were continued in operation.

Air distribution header 98 may be a generally annular member surrounding cupola furnace l0 and also provides supplemental air for the ducts 38 associated with each of the inbed burners positioned on the furnace walls. In this manner a convenient distribution system is provided to supply air to both the afterburners and the auxiliary air supply ducts 38 of the in-bed burners of the present invention. As illustrated in F IG. 4, the gas and air for burners 90 and 30 are supplied from separate sources to permit independent control and operation of the burners.

WHAT IS CLAIMED IS:

1. In a furnace having a charge bed, a stack and a charge door opening within said stack at an elevation above said charge bed, the improvement comprising:

at least one burner mounted on said stack below said charge door opening and adapted to direct a jet of burning gases into said stack below the top surface of said charge bed to provide heat for more complete combustion of products of combustion in said furnace,

means for supplying supplementary air to said charge bed adjacent said igniter to support the combustion of said products,

control means for said supplementary air supply means for directing metered quantities of said supplementary air within said stack, in response to the presence of products of combustion in said stack, to provide substantially full burnout of said products of combustion.

2. The apparatus of claim 1, wherein said igniterbumer comprises a housing adapted to extend into the wall of said cupola stack, a generally cylindrical burner element within said housing, fuel gas supply means communicating with said burner element and means to supply a quantity of air to support combustion within said stack.

3. The apparatus of claim 2, wherein said supplementary air supply means is positioned below said igniter-burner and comprises, a duct communicating with the interior of said furnace and said control means includes at least two banks of damper means, one of said banks being adapted to control the volume of supplementary air supplied to said stack and another of said banks being adapted to control the direction in which said supplementary air is introduced to said stack.

4. The apparatus of claim 1, wherein said supplementary air supply means is inclined downwardly with respect to said stack whereby said air is introduced into said stack at an angle to the stacks vertical axis.

5. The apparatus of claim 2 including at least one afterbumer jet directed into said stack in the vicinity of said charge opening to provide heat for more complete combustion of the products of combustion flowing out of said stack.

6. in a cupola furnace having a charge bed, a stack and a charge opening within said stack at an elevation above said charge bed, the improvement comprising:

a plurality of in-bed burners mounted at spaced peripheral locations about said stack below said charge door opening at a level below the position of the top surface of said charge bed during normal furnace operations,

means for supplying fuel gas and air to said burners for combustion therein whereby said burners direct jets of burning gases into said stack below the top surface of said charge bed to provide heat for more complete combustion of products of combustion in said furnace,

a supplementary air supply duct positioned below each of said burners,

means for supplying air to said supply ducts, and

means for directing and metering quantities of said supplementary air to various sectors in said stack in response to the presence of products of combustion in said sectors, to provide substantially full burnout of said products of combustion.

7. Apparatus as defined in claim 6 wherein said directing and metering means comprises an air supply duct having a plurality of discharge chambers formed therein, said duct including first and second banks of baffles having at least one baffle from each said bank positioned in each of said chambers, the baffles of said first bank being adapted to meter the volume of air flowing through their associated chambers and the baffles of said second bank being adapted to deflect the air flowing in their associated chambers to various sectors of said stack, and means responsive to the presence of products of combustion in said sectors, to control said first and second banks of baffles to supply the necessary air to said sectors for full burnout of said products of combustion.

8. Apparatus as defined in claim 6 wherein said charge bed during normal operation of said furnace includes a relatively porous stack zone and said burners and said supplementary air supply duct, positioned on said stack at a level below the top surface of said charge bed, are adjacent said stack zone during normal operation of said furnace whereby said jets of burning gases and said supplementary air penetrate said charge to insure substantially complete burnout of said products of combustion.

9. A method of reducing air pollution effects of exhaust gases emanating from furnaces having a stack and a charge bed therein, comprising, the steps of,

supplying at least one jet of burning gases to said stack below the top surface of said charge bed to provide heat for attaining and maintaining effective combustion temperatures and achieving more complete combustion of products of combustion in said furnace and for more effectively preheating the charge,

metering and controlling said supply of supplementary air to said stack in response to the composition of exhaust gases in said stack.

10. The method as defined in claim 9, including the step of,

supplying at least one stream of supplementary air to said charge bed to support combustion of said products. 11. The method as defined in claim 9 wherein said supplementary air is supplied to said stack below said jet.

12. The method as defined in claim 1 1 wherein said furnace is a tuyere furnace and said supplementary air is supplied to said stack above said tuyeres.

13. The method of claim 9 including, the step of, combusting unburned carbon monoxide in said furnace stack above said charge bed, said combustion process being initiated by afterbumers directed into said stack in the vicinity of the charging opening of said stack.

14. The method of claim 9 wherein said furnace is a cupola furnace having a charge bed including, a relatively porous stack zone, said jet of burning gases and said supplementary air being supplied to said stack adjacent said stack zone whereby said jets and said air penetrate said charge to insure substantially complete burnout of said products of combustion.

15. The method of claim 9 wherein said furnace is a cupola furnace having a charge bed including, a melting zone, said jet of burning gases and said supplementary air being supplied to said stack adjacent said melting zone with sufficient force to penetrate the charge mass in said zone to insure substantially complete burnout of said products of combustion.

16. A method of improving operation of a furnace containing a charge bed having a plurality of charge composition zones, including a relatively porous stack zone and a charge melting zone, comprising, the steps of,

supplying a plurality of jets of burning gases to said charge below the top surface thereof adjacent said stack zone whereby said jets penetrate said charge to maintain a substantially high temperature within said stack zone and to more effectively preheat the charge in said stack zone prior to entering said melting zone, utilizing the heat of combustion of said jets and from combustion of unburned carbon monoxide to ignite high molecular weight organics in the furnace exhaust gases supplying at least one stream of supplementary air to said charge bed from a position adjacent each of said jets to support combustion of said carbon monoxide and ignition of said organics, and

directing a metered supply of each of said streams of supplementary air to associated sectors of said stack in response to the composition of exhaust gases in said stack.

I SK 

1. In a furnace having a charge bed, a stack and a charge door opening within said stack at an elevation above said charge bed, the improvement comprising: at least one burner mounted on said stack below said charge door opening and adapted to direct a jet of burning gases into said stack below the top surface of said charge bed to provide heat for more complete combustion of products of combustion in said furnace, means for supplying supplementary air to said charge bed adjacent said igniter to support the combustion of said products, control means for said supplementary air supply means for directing metered quantities of said supplementary air within said stack, in response to the presence of products of combustion in said stack, to provide substantially full burnout of said products of combustion.
 2. The apparatus of claim 1, wherein said igniterburner comprises a housing adapted to extend into the wall of said cupolA stack, a generally cylindrical burner element within said housing, fuel gas supply means communicating with said burner element and means to supply a quantity of air to support combustion within said stack.
 3. The apparatus of claim 2, wherein said supplementary air supply means is positioned below said igniter-burner and comprises, a duct communicating with the interior of said furnace and said control means includes at least two banks of damper means, one of said banks being adapted to control the volume of supplementary air supplied to said stack and another of said banks being adapted to control the direction in which said supplementary air is introduced to said stack.
 4. The apparatus of claim 1, wherein said supplementary air supply means is inclined downwardly with respect to said stack whereby said air is introduced into said stack at an angle to the stack''s vertical axis.
 5. The apparatus of claim 2 including at least one afterburner jet directed into said stack in the vicinity of said charge opening to provide heat for more complete combustion of the products of combustion flowing out of said stack.
 6. In a cupola furnace having a charge bed, a stack and a charge opening within said stack at an elevation above said charge bed, the improvement comprising: a plurality of in-bed burners mounted at spaced peripheral locations about said stack below said charge door opening at a level below the position of the top surface of said charge bed during normal furnace operations, means for supplying fuel gas and air to said burners for combustion therein whereby said burners direct jets of burning gases into said stack below the top surface of said charge bed to provide heat for more complete combustion of products of combustion in said furnace, a supplementary air supply duct positioned below each of said burners, means for supplying air to said supply ducts, and means for directing and metering quantities of said supplementary air to various sectors in said stack in response to the presence of products of combustion in said sectors, to provide substantially full burnout of said products of combustion.
 7. Apparatus as defined in claim 6 wherein said directing and metering means comprises an air supply duct having a plurality of discharge chambers formed therein, said duct including first and second banks of baffles having at least one baffle from each said bank positioned in each of said chambers, the baffles of said first bank being adapted to meter the volume of air flowing through their associated chambers and the baffles of said second bank being adapted to deflect the air flowing in their associated chambers to various sectors of said stack, and means responsive to the presence of products of combustion in said sectors, to control said first and second banks of baffles to supply the necessary air to said sectors for full burnout of said products of combustion.
 8. Apparatus as defined in claim 6 wherein said charge bed during normal operation of said furnace includes a relatively porous stack zone and said burners and said supplementary air supply duct, positioned on said stack at a level below the top surface of said charge bed, are adjacent said stack zone during normal operation of said furnace whereby said jets of burning gases and said supplementary air penetrate said charge to insure substantially complete burnout of said products of combustion.
 9. A method of reducing air pollution effects of exhaust gases emanating from furnaces having a stack and a charge bed therein, comprising, the steps of, supplying at least one jet of burning gases to said stack below the top surface of said charge bed to provide heat for attaining and maintaining effective combustion temperatures and achieving more complete combustion of products of combustion in said furnace and for more effectively preheating the charge, metering and controlling said supply of supplementary air to said stack in response to the composition of exhAust gases in said stack.
 10. The method as defined in claim 9, including the step of, supplying at least one stream of supplementary air to said charge bed to support combustion of said products.
 11. The method as defined in claim 9 wherein said supplementary air is supplied to said stack below said jet.
 12. The method as defined in claim 11 wherein said furnace is a tuyere furnace and said supplementary air is supplied to said stack above said tuyeres.
 13. The method of claim 9 including, the step of, combusting unburned carbon monoxide in said furnace stack above said charge bed, said combustion process being initiated by afterburners directed into said stack in the vicinity of the charging opening of said stack.
 14. The method of claim 9 wherein said furnace is a cupola furnace having a charge bed including, a relatively porous stack zone, said jet of burning gases and said supplementary air being supplied to said stack adjacent said stack zone whereby said jets and said air penetrate said charge to insure substantially complete burnout of said products of combustion.
 15. The method of claim 9 wherein said furnace is a cupola furnace having a charge bed including, a melting zone, said jet of burning gases and said supplementary air being supplied to said stack adjacent said melting zone with sufficient force to penetrate the charge mass in said zone to insure substantially complete burnout of said products of combustion.
 16. A method of improving operation of a furnace containing a charge bed having a plurality of charge composition zones, including a relatively porous stack zone and a charge melting zone, comprising, the steps of, supplying a plurality of jets of burning gases to said charge below the top surface thereof adjacent said stack zone whereby said jets penetrate said charge to maintain a substantially high temperature within said stack zone and to more effectively preheat the charge in said stack zone prior to entering said melting zone, utilizing the heat of combustion of said jets and from combustion of unburned carbon monoxide to ignite high molecular weight organics in the furnace exhaust gases supplying at least one stream of supplementary air to said charge bed from a position adjacent each of said jets to support combustion of said carbon monoxide and ignition of said organics, and directing a metered supply of each of said streams of supplementary air to associated sectors of said stack in response to the composition of exhaust gases in said stack. 